Diet differences between wild and stocked age-0 to age-3 lake trout indicate influence of early rearing environments

Abstract

Wild lake trout recently began to appear in abundance in Lake Champlain after over 40 years of stocking, providing an opportunity to compare the seasonal diet of wild and stocked juveniles. We sampled 2,349 age-0 to age-3 lake trout collected in bottom trawls from April to November 2015–2018, and examined the relationship between diet and spatial heterogeneity in abundance of wild and stocked juveniles. Stocked fish were, on average, the size of wild fish one year older. Wild juveniles had fewer empty stomachs and more items per stomach than stocked fish at each age. Mysis diluviana dominated the diet of age-0 and age-1 wild lake trout until they began to consume fish in fall at age-1. In contrast, the diet of newly-stocked fish (age-1) comprised rainbow smelt (Osmerus mordax), slimy sculpin (Cottus cognatus), alewife (Alosa pseudoharengus), with Mysis only abundant in summer and fall. Number and composition of diet items varied among geographic areas of the lake but did not explain differences in abundance of wild or stocked fish by area. Diet overlap was high between wild and stocked fish for each age class at each season, except in fall at age-0. Differences in the diet of wild and stocked juveniles likely reflect effects of early rearing experience. Recruitment of wild lake trout depends on availability and abundance of Mysis, but our diet data do not provide insight to explain why recruitment is finally occurring after a protracted delay.